The mechanism of oxidative phosphorylation was and has remained one of the most challenging problems in biochemistry. Central to the elucidation of the mechanism of this pathway is a complete understanding of the functional and structural properties of mitochondrial ATPase (ATP synthetase), and enzyme system that catalyses the last of the oxidative phosphorylation reactions. Crystals of the soluble portion of this enzyme (F1-ATPase) were obtained in our laboratory and the structure is being studied at 9 A resolution. In this project we propose to continue our single crystal X-ray diffraction studies of the determination of the three-dimensional structure of the F1-sector of the ATP synthetase from rat liver mitochondria. Our present results will be extended through the inclusion of diffraction data to 3.5 A resolution. The structures of the complexes of F1-ATPase with substrates, products and effectors (or their analogs) will also be determined. The determination of these structures will address in a very direct way some of the outstanding questions in oxidative phosphorylation and provide invaluable information for the understanding of ATP-dependent ion translocation processes.